Electro-optic device for improving reading ability

ABSTRACT

An electro-optic device for improving reading ability comprises reading matter over which is placed a pair of parallel transparent insulating plates forming a sandwich, each of the plates being coated on the inside surface with a spaced array of parallel closely-spaced transparent electrode bands, the direction of the bands on one plate being disposed perpendicularly to and insulated from those on the other, the electrode crossings thus forming a series of rows of separate reading panels disposed in register with the reading matter. A thin layer of transparent insulating material covers the coated surface of at least one plate and a thin layer of transparent nematic liquid crystal composition capable of entering a stage of non-destructive opacity, when subjected to a threshold voltage, is disposed between the plates. A source of voltage is provided to impress a variable voltage across the electrodes, the voltage ranging from below the threshold value of the nematic liquid to a voltage above the saturation value, and sequential switching means is connected between the voltage source and the electrodes and it is designed, first, to impress at least a saturation voltage on the panels whereby they become opaque with respect to the reading matter, and then sequentially to reduce the voltage on the panels to below the threshold value, in reading relation, whereby the panels are made sequentially transparent.

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Whitcomb et al. July 31, 1973 ELECTRO-OPTIC DEVICE FOR paralleltransparent insulating plates forming a sand- IMPROVING READING ABILITYWich, each of the plates being coated on the inside surface with aspaced array of parallel closely-spaced Path Joseph w Raba 3O Peachtreetransparent electrode bands, the direction of the bands on one platebeing disposed perpendicularly to and inboth of Huntington 1 I746sulated from those on the other, the electrode crossings [22] Filed:Feb. 15, 1972 thus forming a series of rows of separate reading panelsdisposed in register with the reading matter. A thin [21] Appl' 226459layer of transparent insulating material covers the coated surface of atleast one plate and a thin layer of [76] Inventors: Elmer W. Whitcomb,74 E. Rogues [52] US. Cl 35/35 B, 350/160 R transparent nematic liquidcrystal composition capable [5l] Int. Cl. G09b 17/02, 00% 17/04 ofentering a stage of non-destructive opacity, when [58] Field of Search350/160 LC; 35/35 B subjected to a threshold voltage, is disposedbetween the plates. A source of voltage is provided to impress [56]References Cited a variable voltage across the electrodes, the voltageUNITED STATES PATENTS ranging from below the threshold value of thenematic 2,535,243 12/1950 Taylor 35/35 B a f l above l Saturatio" valueand 2,782,528 2/1957 wast] t t H 35/35 B quential switching means isconnected between the 3,322,485 5/1967 Williams 350/160 LC voltageSource and the electrodes and it is designed, 3,499,112 3 1970l-leilmeier et a]. 350/160 LC fi to pr a least a saturation voltage onthe p 3,674,342 7/1972 Castellano et al. 350/160 LC els whereby theybecome opaque with respect to the reading matter, and then sequentiallyto reduce the Primary Examiner-R0nald L. Wibert voltage on the panels tobelow the threshold value, in AttorneyPeter J. Gaylor reading relation,whereby the panels are made sequentially transparent. [57] ABSTRACT Anelectro-optic device for improving reading ability comprises readingmatter over which is placed a pair of 12 Claims, 6 Drawing FiguresPAIENIEU JUL 31 ms SHEEE 2 fi 2 M. & m llllll .i m W O PW I JIII}V FIG.

I I/III/I/I/I/IIIn/l/ BACKGROUND OF THE INVENTION This invention dealswith an electro-optic device to improve reading ability. Prior artreading machines, practically all of which have been based onmechanical-optic arrangements, have been subject to many disadvantages.Some employ optical projection at atypical reading distances. Others areaudibly disturbing to the user as well as to other individuals. Many arenot readily portable. A number of them do not provide a true horizontalattack and, if they do, the reading material is not presented in amanner consistent with natural saccadic eye movements. Otherdisadvantages of such prior art machines include poor, or lack of,adjustability for the span of recognition and duration of fixation, andneed for specially printed material, inability to operate with ordinaryreading light, and necessity for a darkened room.

A search of the prior art revealed U.S. Pat. No. 3,322,485 whichdiscloses an electro-optical element using an organic nematic liquid formaking optical displays. Although seguential and cyclical energizationof the conductive electrodes are mentioned, these are done for formingcharacters, or for the formation of a picture display, wherein theopaque form of the nematic liquid is the utile form when backgroundreflection is not required, whereas, in the present invention, thetransparent form of the nematic liquid is employed in effecting thereading operation.

In U.S. Pat. No. 3,499,l 12, an electro-optical device employs a glasssandwich between which a nematic liquid crystal is subjected to avoltage field for optical display purposes. Here, also, innon-reflection applications, the turbulent or opaque condition of theliquid crystal is the utile form.

Other U.S. Pat., such as Nos. 3,503,672, 3,503,673 and 3,519,330 havebeen directed to electric pulsing or bias involving nematic liquidcrystals, but they, also, 40

have employed such operations for forming opaque displays as the usefulproducts of their operations.

SUMMARY OF THE INVENTION According to the present invention, a silent,portable, easily-adjustable reading device is provided for trainingindividuals to read rapidly by directing saccadic eye movements. One ofthe main features of the invention is a sandwich of glass or othertransparent insulating material provided with separate reading areaportions, the transparency of which may be controlled and sequenced soas to move, for example, as the eye moves saccadically along a line ofprinted matter (the latter being disposed in register under saidsandwich and made visible when said area portions are made transparent).

The sandwich, otherwise referred to as the electrooptic unit, contains athin layer ofgamatic liquid crystal composition (light valve) whichurTderg'otiorefiiibits an essentially non-destructive turbulence oropacity when subjected to an electric voltage. This turbulence, which isrestricted only to the area of applied voltage, causes an efficientscattering of light (dynamic scattering) incident to that region, thusmaking opaque the nematic layer in that region, so that the readingmatter disposed underneath is not discernable. The degree of lightscattering may be varied by changing the impressed voltagebetween aminimum threshold value needed to initiate the turbulence, to asaturation value above which there is very little, if any furtherscatter- BRIEF DESCRIPTION OF THE DRAWINGS The invention will be morereadily understood by reference to the accompanying drawings in which apreferred embodiment is described, and in which:

FIG. 1 shows a front elevational view, partly in stripped form, of asandwich viewing plate of the present invention;

FIG. 2 presents an enlarged cross-sectional side view of the plate shownin FIG. 1;

FIG. 3 shows a corner portion of a substrate plate, in dicating how leadconnections are attached thereto;

FIG. 4 depicts a front elevational view of a stand holding a sheet ofprinted matter and a viewing plate disposed thereover for sequentialreading of the printed matter at a desired speed;

FIG. 5 illustrates a side elevational view of the unit shown in FIG. 4,and

FIG. 6 is a rear elevational view of a part of the stand of that of FIG.4, withthe back panel cut away.

The same numerals refer to the same or similar parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The sandwich view plate(electro-optic unit) of the present invention is exemplified by thatindicated generally in FIGS. 1 and 2. Rear glass plate 10 is completelycoated on its inside surface with a transparent conductive layer 11 oftin oxide, or the like. Then, vertical scoring lines 12 are made with asharp tool, at regularly-spaced intervals, penetrating and removing theconductive layer 11, thus producing vertical lines 12 of insulation ofabout 0.01 inch width, or even less, thereby providing separate verticalstrip or band electrodes 11, I 1", etc. To the naked eye, the glasssurface does not reveal any discontinuity in such a case. Each electrodeis provided with a lead, such as leads l3, 13, 13 etc.

The inner surface of the top plate 16 is likewise coated with a layer ofconductive transparent material, such as layer 11a, and the layeredsurface is likewise scored, but with horizontal scoring lines 17, thusproviding horizontal conductive band electrodes 18, 18', 18", etc. Leads19, l9, 19', etc., are connected to the ends of the horizontalelectrodes.

The inner surface of coated glass plate 16 is then covered with a thinfilm or sheet of insulating plastic 15, and the plates are assembledinto a sandwich 30, as in FIGS. 1 and 2. Spacers or shims 35 aredisposed at the edges between the plates to provide a space of less than0.001 inch, and, desirably, about 0.0005 inch width, in which the thinfilm 14 of nematic liquid is contained. This space should be completelyfilled with the liquid. When proper voltage is applied on both thevertical and horizontal electrodes, the turbulence or opacity of thenematic liquid 14 takes place at the overlap or crossing of an energizedvertical electrode with an energized horizontal electrode, therebycreating a prospective reading panel, such as panel 20, 20', or 20".Both insulated vertical leads 13, 13', 13", etc., and horizontal leadsl9, 19', 19', etc., are gathered into a cable 21.

The manner of connecting the leads to the electrode ends ofelectro-optic unit 30 is described in FIG. 3.

Glass plate 16, on which conductive coating 11a is deposited, has a verythin conductive (e.g., copper) clip 36 attached in contact with coating11a. The end 37 of lead 19 was previously soldered to the conductiveclip and the junction of the clip and the coating is secured by use of aconducting epoxy cement 38.

When in operation, switch 26 (FIG. is turned on, thus energizing allelectrodes to above the threshold value, thereby making opaque allpanels 20, 20, 20", etc., of sandwich plate 30, and the reading matteron the exposed page of book 24 is not visible to the reader. By use ofthree fixed voltages, an electric grid pattern is arranged so as tocause the voltage at the overlap between any given pairs of electrodesto fall below the threshold level, whereby such panels 20, 20', 20",etc., become successively transparent, thus enabling the viewer to readthe page of book 24. Since all of the other electrode crossings havefields above the saturation level, they remain opaque. Hence, by propercom mand sequencing, the transparent area can be moved from panel topanel, horizontally along a reading line, or along two or more lines ofany desired height, or vertically along one, two or more columns of anydesired width, or any desired combination thereof. Conventionalarrangements may be effected to provide for the required switchingfunction to cause the opaque reading area to become transparent in anydesired sequence. Conventional mechanical, electronic orelectro-mechanical switching means may be employed to effect thisswitching function.

In order to explain this switching procedure, we can assume that thedynamic scattering saturation for a particular nematic liquid crystalcomposition and configuration employed would be, say, 100 volts for thespacing used. There may be provided three voltages: Plus 50, minus 50and plus 150 volts. At the outset, the voltage at all electrodecrossings can be made to be 100 volts or more, which is above thesaturation value for effecting the dynamic scattering. With such avoltage applied, all panels 20, 20, 20", etc., of the reading plate 30will be opaque to the reading matter behind the panel. Now, ifelectrodes 19,19, 19", etc., and 13, l3, 13'', etc., are sequentiallyswitched so as to result in a zero voltage at the crossings, thepanels20, 20, 20", etc., will become sequentially transparent, thus making thereading matter, such as XX in FIG. 1, visible to the reader. Because therest of the panels have a voltage above the saturation value impressedacross the vertical and horizontal leads and electrodes, the nematicliquid therein will be subjected to dynamic scattering, so that thepanels will remain opaque. It is thus possible to effect a sequentialvoltage switching for the panels 20, 20', 20",'etc., and, by turningknob 31, any desired controlled sequential speed may be attained toenable the saccadic movements of the readers eyes to read thetransparentized" areas of the sandwich as they become exposed.

As is apparent from the foregoing, it is possible to transparentize thepanels either horizontally or vertically, or in any desired pattern, andin any desired width or height, as well as at any desired speed. It is,of course, essential that the nematic liquid crystal composition be onewhich will have a suitable response speed, i.e., opacity to transparencyconversion rate, and vice versa, without any objectionable time lag forthe speeds selected.

In FIGS. 4-6, a viewing plate, of the type illustrated in FIGS. l-2, isshown as employed for reading use. A stand 22, made of wood, plastic, orother suitable material, has a tilted (up to vertical position) forwardface 23, on which may be placed the open book 24, or other printedmatter to be read. A projecting lipped edge 25 extending from the bottomof the stand serves to support the book. The viewing plate 30 isdisposed over the open page of book 24. Cover 33 serves to protect theotherwise exposed leads of the horizontal electrodes if they are notcontained in the sandwich.

Cable 21 is lead into the inside of stand 22, wherein are mounted switch26, transformer 27, sequential switch 28 with motor 29 for commutatorrotation and with turn dial 31, and other electrical elements. All ofthe electrical elements are of conventional type and sequentialswitching is also conventional and may be similar to that employed in USPat. No. 3,499,112. Electric lead 32 is connected to a source ofelectric power. Back panel 32 of stand 22 is partially cut away in FIG.6.

The prior art on nematic displays specifies that the electrodes must bein direct contact with the liquid crystal material, thus necessitatingthe use of relatively thick liquid crystal films to avoidinter-electrode shorting between plates. However, for the purpose of thepresent invention, very thin films of the nematic liquid are necessary.One reason is that the nematic liquid, even in its non-turbulent state,is not water clear. Furthermore, when very thin films of such liquidcrystals are used in direct contact with bare electrodes, it is verydifficult to prevent inter-electrode arcing.

Although some of the display prior art refers to the desirability ofthin films of5 to 15 micron thickness for the nematic liquid, it isnoteworthy that, in describing their actual devices for display use,they specify thicknesses of l or A mm., which is 50 to lOO times greaterthan the desired thickness, thereby indicating the inability to achievea practical display with the thin films desired.

Fortunately, it has been found that dynamic scattering of the liquidcrystal may be effectively initiated without direct contact of theliquid crystal with the electrodes. This finding makes it possible toinsulate very effectively with very thin film transparent insulation,either the horizontal or the vertical (directional) electrodes, or both,and still obtain the required opacity, thus making it possible for thereader to see well through the very thin nematic liquid layer of thesandwich structure.

It is desirable that the transparent substrate plates 10 and 16 of thesandwich have parallel inner faces to insure against arcing betweenelectrodes. The most desirable materials for the purpose are glassplates, the surfaces of which have been ground or otherwise formed, toinsure parallelism. The surface of the upper plate may be conventionallytreated to eliminate reflection problems. Other plate materials whichmay be used are plastic sheets, such as those made of polymethylmethacrylate, sold under the trademark Lucite," as well as othertransparent plate materials. It is, of course, necessary that suchplates be insoluble in the nematic liquid employed, and not subject toany other adverse effects therefrom.

The nematic liquid crystal composition used in the present invention maybe any one, or a combination, of the compounds described in US Pat. Nos.3,322,485,

3,499,702 and 3,540,796. However, it is preferred to use liquid crystalcompositions which will convert from opacity to transparency, and viceversa, at room temperatures. An example of such a material isp-methoxybenzylidine, p-n-butyl aniline (4-methoxy-4-n-butylbenzilidineaniline), marketed commercially under the trademark MBBA and having amolecular weight of 267.39 and an average refractive index of 1.60. Itsnematic temperature range is to 48 C, and it exhibits a strongbirefringence and a high dispersion. Although such compositions aremilky in appearance when viewed in their containers, they aretransparent when employed in the form of very thin films used herein.

In the sandwich 30, the nematic crystal layer 14 is desirably of athickness of not over about 0.001 inch and desirably 0.0005 inch, oreven less. Since nematic compositions are now available having anopacitytransparency conversion (exposure) rate of about 30 frames persecond, this value is adequate for the present purpose.

The material suitable for the preparation of the transparent electrodes(e.g., 11' or 18), of the present invention, may be a film of molybdenumoxide, about 1.0 micron in thickness, which is thermally evaporated byconventional means at a pressure of about 10 torr. However, a preferredmaterial for this purpose is a transparent indium oxide or tin oxidefilm material marketed commercially under the trademark Nesatron. It is,of course, possible to coat or otherwise form the inside surfaces ofsaid substrate plates with the parallel electrodes by use of a mask.

The non-conductive material used for covering one or more series ofdirectional electrodes may be made of varnish, resin, deposited silicondioxide, glass, or the like. One of the most desirable materials forthis purpose is a very thin sheet of insulating plastic, such aspolyethylene terephthalate, marketed commercially under the trademarkMylar C. This sheet material, which may have a thickness of about 0.0003inch to about 0.0005 inch, is employed to cover all surfaces of eitheror both directional electrodes. Another suitable film for such use is aplastic sheet sold commercially under the trademark Saran."

In operation, when reading matter is being sequentiallytransparentized," it is possible either to allow the already-read matterto remain transparent, or to merely sequentially transparentize thematter to be read, while all of the remaining panels are opaque.Switching procedures for effecting such procedures are well known in theart.

We claim:

1. An electro-optic device disposable over a sheet of reading matter forimproving reading ability, comprismg:

a pair of transparent insulating plates forming a sandwich, each of saidplates having a coating on the inside surface of a spaced array ofparallel transparent electrode bands, the electrode bands on one platebeing disposed perpendicularly to those on the other, said spacedelectrode bands forming at their crossings, a series of rows of separatereading panels disposed in register with said reading matter,

a thin layer of transparent insulating material covering theelectrode-coated surface of at least one plate, a thin layer oftransparent nematic liquid crystal composition having the property ofentering a stage of non-destructive opacity when subjected to athreshold voltage disposedbetween said plates,

a source of electric voltage designed to impress a variable voltagethrough said electrode bands and across said sandwich, said voltageranging from below the threshold value to above the saturation value ofsaid nematic liquid, and sequential switching means connected betweensaid voltage source and said electrode bands and designed first toimpress at least a saturation voltageon said panels whereby they becomeopaque with respect to said reading matter, and then sequentially toreduce said voltage on said panels to below the threshold value inreading relation, whereby said panels are made sequentially transparentto make visible said reading matter in reading relation.

2. An electro-optic device, according to claim 1, wherein said electrodebands are separated by an insulating scoring line.

3. An electro-optic device, according to claim 1, in which said layer ofinsulating material comprises a thin sheet of plastic having a thicknessof not over about 0.0005 inch.

4. An electro-optic device, according to claim 1, in which said layer ofnematic liquid has a thickness of not over 0.001 inch.

5. An electro-optic device for improving reading ability, comprising:

a sheet of reading matter,

a pair of parallel transparent insulating plates forming a sandwich,each of said plates having a coating on the inside surface of a spacedarray of parallel transparent electrode bands, the electrode bands onone plate being disposed perpendicularly to those on the other, saidspaced electrode bands forming, at their crossings, a series of rows ofseparate reading panels disposed in register with said reading matter,

a thin layer of transparent insulating material covering the coatedinside surface of at least one plate,

a thin layer of transparentnematic liquid crystal composition having theproperty of entering a stage of non-destructive opacity when subjectedto a threshold voltage disposed between said plates,

a source of electrical voltage designed to impress a variable voltagethrough said electrode bands and across said sandwich, said voltageranging from below the threshold value to above the saturation value ofsaid nematic liquid, and sequential switching means connected betweensaid voltage source and said electrode bands and designed first toimpress at least a saturation voltage on said panels whereby they becomeopaque with respect to said reading matter, and the sequentially toreduce said voltage on said panels to below the threshold value inreading relation, whereby said panels are made sequentially transparentto make visible said reading matter in reating relation.

6. An electro-optic device, according to claim 5, in which said layer ofnematic liquid has a thickness of not over about 0.001 inch.

7. An electro-optic device, according to claim 5, wherein said layer ofinsulating material comprises a layer of sheet plastic having athickness of not over about 0.0005 inch.

reading relation, whereby said panels are made sequentially transparentto make visible said printed matter in reading relation. 10. Anelectro-optic device, according to claim 9, having switching speedcontrol means for varying the speed of said sequential switching.

8. An electro-optic device, according to claim 5, wherein said electrodebands comprise wide bands separated from each other by insulatingscoring lines.

9. An electro-optic device for improving reading ability, comprising:

a stand having a raised forward face and protruding bottom retainingmeans on which a sheet of printed matter may be supported, a sandwichreading plate disposable on said retaining means and over said below thethreshold value to above the saturation value of said nematic liquid,and

11. A process for improving reading ability, comprising:

placing, over a sheet of reading matter, a pair of par Primed matter andcomprislflgz 10 allel transparent insulating plates forming a sand- 3 Pof Parallel transparentfnsulatmg plates form wich, each of said platesbeing coated on the inside z :1::Y iz$ sfgi zg zggzi2:25 2:32; surfacewith a spaced array of parallel transparent electrode bands thedirection of the electrode allel trans arent electrode bands thedirection of the electr de bands on one plate being disposed bands onone plate bemg dlsposed perpendlcslary to those on the other, saidspaced electrode an s 2352;152:151@2232;isis t ssssifgz zsi at of ofries of rows of separate reading panels disposable rate panels disposedregister over sald reading in register over said primed matter matter,the coated inside surface of at least one a thin layer of transparentinsulating material cov- .plate bgmg covefed with of i transpilrem eringthe coated inside surface of at least one insulating plastic, and saidsandwich enclosing a plate thin layer of transparent nematic liquidcrystal e s a e a thin layer of transparent nematic liquid crystalcomposmon havlng the ploperty of emrmgastage composition having theproperty of entering a of HOI'bdCSU'UCtIVC opacity when sub ected to astage of non-destructive opacity when subjected 25 reshold voltage,impressing an electrical voltage to a threshold voltage disposed betweenSaid above the saturation value on said electrode bands, plates, wherebysaid panels are made opaque to said reada source of electric voltagedesigned to impress 9. mg mfmer, f

variable voltage through said electrode bands and Sequemlally SwltchmgSald voltage to below across said Sandwich said voltage ranging fthreshold value on said panels, in reading relation,

whereby said panels are made sequentially transparent, and the saidreading matter is thus made visible in reading relation.

sequential switching means mounted on said stand and connected betweensaid voltage source and said electrode bands and designed first toimpress at least a saturation voltage on said panels whereby they becomeopaque with respect to said printed matter, and then sequentially toreduce said volt- 12. A process, according to claim 11, wherein theelectrode bands are made by coating the insulating plates with atransparent conductive layer, and then scoring the layered surfaces atspaced intervals to provide insulated bands thereon.

age on said panels to below the threshold value, in

2. An electro-optic device, according to claim 1, wherein said electrodebands are separated by an insulating scoring line.
 3. An electro-opticdevice, according to claim 1, in which said layer of insulating materialcomprises a thin sheet of plastic having a thickness of not over about0.0005 inch.
 4. An electro-optic device, according to claim 1, in whichsaid layer of nematic liquid has a thickness of not over 0.001 inch. 5.An electro-optic device for improving reading ability, comprising: asheet of reading matter, a pair of parallel transparent insulatingplates forming a sandwich, each of said plates having a coating on theinside surface of a spaced array of parallel transparent electrodebands, the electrode bands on one plate being disposed perpendicularlyto those on the other, said spaced electrode bands forming, at theircrossings, a series of rows of separate reading panels disposed inregister with said reading matter, a thin layer of transparentinsulating material covering the coated inside surface of at least oneplate, a thin layer of transparent nematic liquid crystal compositionhaving the property of entering a stage of non-destructive opacity whensubjected to a threshold voltage disposed between said plates, a sourceof electrical voltage designed to impress a variable voltage throughsaid electrode bands and across said sandwich, said voltage ranging frombelow the threshold value to above the saturation value of said nematicliquid, and sequential switching means connected between said voltagesource and said electrode bands and designed first to impress at least asaturation voltage on said panels whereby they become opaque withrespect to said reading matter, and the sequentially to reduce saidvoltage on said panels to below the threshold value in reading relation,whereby said panels are made sequentially transparent to make visiblesaid reading matter in reating relation.
 6. An electro-optic device,according to claim 5, in which said layer of nematic liquid has athickness of not over about 0.001 inch.
 7. An electro-optic device,according to claim 5, wherein said layer of insulating materialcomprises a layer of sheet plastic having a thickness of not over about0.0005 inch.
 8. An electro-optic device, according to claim 5, whereinsaid electrode bands comprise wide bands separated from each other byinsulating scoring lines.
 9. An electro-optic device for improvingreading ability, comprising: a stand having a raised forward face andprotruding bottom retaining means on which a sheet of printed matter maybe supported, a sandwich reading plate disposable on said retainingmeans and over said printed matter and comprising: a pair of paralleltransparent insulating plates forming a sandwich, each of said plateshaving a coating on the inside surface of a spaced array of paralleltransparent electrode bands, the direction of the electrode bands on oneplate being disposed perpendicularly to those of the other, said spacedelectrode bands forming, at their crossings, a series of rows ofseparate reading panels disposable in register over said printed matter,a thin layer of transparent insulating material covering the coatedinside surface of at least one plate, a thin layer of transparentnematic liquid crystal composition having the property of entering astage of non-destructive opacity when subjected to a threshold voltagedisposed between said plates, a source of electric voltage designed toimpress a variable voltage through said electrode bands and across saidsandwich, said voltage ranging from below the threshold value to abovethe saturation value of said nematic liquid, and sequential switchingmeans mounted on said stand and connected between said voltage sourceand said electrode bands and designed first to impress at least asaturation voltage on said panels whereby they become opaque withrespect to said printed matter, and then sequentially to reduce saidvoltage on said panels to below the threshold value, in readingrelation, whereby said panels are made sequentially transparent to makevisible said printed matter in reading relation.
 10. An electro-opticdevice, according to claim 9, having switching speed control means forvarying the speed of said sequential switching.
 11. A process forimproving reading ability, comprising: placing, over a sheet of readingmatter, a pair of parallel transparent insulating plates forming asandwich, each of said plates being coated on the inside surface with aspaced array of parallel transparent electrode bands, the direction ofthe electrode bands on one plate being disposed perpendicularly to thoseon the other, said spaced electrode bands forming, at their crossings, aseries of rows of separate panels disposed in register over said readingmatter, the coated inside surface of at least one plate being coveredwith a sheet of thin transparent insulating plastic, and said sandwichenclosing a thin layer of transparent nematic liquid crystal compositionhaving the property of entering a stage of non-destructive opacity whensubjected to a threshold voltage, impressing an electrical voltage abovethe saturation value on said electrode bands, whereby said panels aremade opaque to said reading matter, and sequentially switching saidvoltage to below said threshold value on said panels, in readingrelation, whereby said panels are made sequentially transparent, and thesaid reading matter is thus made visible in reading relation.
 12. Aprocess, according to claim 11, wherein the electrode bands are made bycoating the insulating plates with a transparent conductive layer, andthen scoring the layered surfaces at spaced intervals to provideinsulated bands thereon.